1. Technical Field
The present invention relates to a liquid ejecting head (such as an ink jet type recording head) and a liquid ejecting apparatus. The invention particularly relates to a liquid ejecting head which ejects liquid introduced to a pressure chamber from a liquid supply path, from a nozzle, and relates to a liquid ejecting apparatus.
2. Related Art
A liquid ejecting apparatus includes a liquid ejecting head which can eject liquid as liquid droplets from a nozzle. The liquid ejecting apparatus is an apparatus which ejects various types of liquid from the liquid ejecting head. Representative examples of the liquid ejecting apparatus include an image recording apparatus, such as an ink jet type recording apparatus (printer) which has an ink jet type recording head (hereinafter, referred to as a recording head), ejects liquid ink as ink droplets from the nozzle of the recording head, and performs recording. In addition, other than that, the liquid ejecting apparatus is used in ejecting various types of liquid, such as a coloring material used in a color filter of a liquid crystal display or the like, an organic material used in an organic Electro Luminescence (EL) display, or an electrode material used in forming an electrode. At the recording head for the image recording apparatus, the liquid ink is ejected. At a coloring material ejecting head for a display manufacturing apparatus, a solution of each coloring material of Red (R), Green (G), and Blue (B) is ejected. In addition, at an electrode material ejecting head for an electrode forming apparatus, a liquid electrode material is ejected. At a bio-organic material ejecting head for a chip manufacturing apparatus, a solution of a bio-organic material is ejected.
Inside the liquid ejecting head (which employs an ink jet technology) are provided a plurality of nozzles, a pressure chamber formed in each nozzle, a common liquid chamber (referred to as a reservoir or a manifold) which is common to the plurality of pressure chambers, a liquid supply path which respectively communicates with the common liquid chamber and each of the pressure chambers, and the like. By driving pressure generating means, such as a piezoelectric element or a heating element, a pressure change is applied to a liquid in the pressure chamber, and the liquid ejecting head is configured to eject the liquid from the nozzle by using the pressure change.
As the liquid ejecting head, various configurations are suggested. For example, a liquid ejecting head (ink jet type recording head) disclosed in JP-A-2001-293864 has a so-called longitudinal vibration type piezoelectric vibrator which vibrates in a longitudinal direction (a direction which is orthogonal to an electric field direction) of the piezoelectric vibrator) as a pressure generating means. After laminating and curing a piezoelectric body layer made of zirconia or lead zirconate titanate having an electrode layer at a surface thereof, the piezoelectric vibrator is manufactured through a step of dividing into a combtooth shape. Each one of the divided combteeth functions as the piezoelectric vibrator corresponding to each pressure chamber. The longitudinal vibration type piezoelectric vibrator is difficult to be made small, and is generally mounted on a comparatively large liquid ejecting head. In that type of the liquid ejecting head, an established pitch of the nozzles has an interval equivalent to, for example, 1/180 inches (that is, approximately 141 μm). Corresponding to this, it is possible to ensure a comparatively large capacity of a flow path of the pressure chamber or the like which communicates with the nozzle.
In contrast, a liquid ejecting head disclosed in JP-A-2003-231254 is made smaller than the liquid ejecting head disclosed in JP-A-2001-293864. The piezoelectric vibrator used in the liquid ejecting head is configured to have respectively laminated and formed a lower electrode, a piezoelectric body layer made of a piezoelectric material, and an upper electrode by a film forming technology (and to be divided for every pressure chamber by patterning by etching such as lithography), and ion milling. The piezoelectric vibrator is a so-called bending vibration type piezoelectric vibrator which is bent and deformed in the electric field direction. Compared to the above-described longitudinal vibration type piezoelectric vibrator, the bending vibration type piezoelectric vibrator can be made smaller. For this reason, the bending vibration type piezoelectric vibrator contributes to having a smaller sized liquid ejecting head on which the piezoelectric vibrator is mounted as pressure generating means. In the type of liquid ejecting head, the established pitch (distance between the centers) of the nozzles has an interval equivalent to, for example, 1/300 inches (that is, approximately 84.66 μm). Compared to JP-A-2001-293864, higher density of the nozzles can be achieved. For this reason, the capacity of the flow path of the pressure chamber or the like is limited.
However, in the type of liquid ejecting head, since the liquid (meniscus) in the nozzle is exposed to outside air, a solvent component included in the liquid evaporates, and the liquid thickens with passage of time. As the recording head disclosed in JP-A-2003-231254, the small-sized liquid ejecting head, of which the nozzles are formed in a high density, relates to the capacity of the pressure chamber and is smaller compared to the recording head which is comparatively large disclosed in JP-A-2001-293864. For this reason, in the small-sized liquid ejecting head, the liquid is comparatively likely to thicken from a nozzle side to the inside of the pressure chamber. When the liquid inside the pressure chamber thickens, ejection characteristics (such as an amount of the liquid ejected from the nozzle, or a flying speed (flying direction)) changes from an ideal state. In order to reduce such defects, in the liquid ejecting apparatus provided with such a liquid ejecting head (recording head), for example, a maintenance process (flushing process) is performed in which the liquid is forced to be ejected from the nozzle regularly during a recording process (ejecting process) with respect to a recording medium (landing object of the liquid), and the thickened liquid is discharged. However, in the flushing process, a printing process is temporarily suspended, the liquid is moved to a flushing point, and the liquid is discarded from all of the nozzles. Therefore, if the flushing process is performed frequently, there are problems that a processing capability (throughput) per unit time is deteriorated during the printing process, and the liquid is uselessly consumed.
When progress of thickening changes the interval of performing the flushing process in the small-sized recording head (to be described in detail, for example, a head B or C in FIG. 3), a rate of discharging of liquid (necessary consumption amount of the liquid in eliminating thickening) which is necessary in the flushing process is high. In other words, a performance of the liquid ejecting head is likely to be influenced by a length of the flushing interval. For this reason, when the liquid ejecting head is mounted on the liquid ejecting apparatus, it is necessary to specifically set the flushing interval to be within a comparatively short range, and there is a problem that it is hard to handle the liquid ejecting head.